The subject invention pertains to polyether polyols and the polyurethane foams which may be prepared therefrom. More particularly, the subject invention pertains to certain 1,2-diaminocycloalkane-initiated polyoxyalkylene polymers which have unusually low levels of unsaturation. These polyethers may be used to prepare polyurethane foams without resort to blowing agents containing chlorofluorocarbons. 2. Description of the Related Art
Polyoxyalkylene polyether polyols are well established as raw materials for polyurethane foams. These polyether polyols are easily prepared by the base catalysed addition of an oxirane onto a polyhydric initiator molecule whose active hydrogens are capable of reacting with the oxirane in a ring opening polymerization. Such active hydrogens are generally contained in hydroxyl and amino groups. Oxirane and methyloxirane are the preferred oxiranes, with the former yielding a primary hydroxyl terminal group while the latter yields a secondary hydroxyl group.
It is well known that allylic unsaturation is formed during the polymerization of propylene oxide, and mechanisms for its formation are discussed in Block and Graft Polymerization, Vol. 2, Ceresa, Ed., John Wiley & Sons, on pages 17-21. Whatever the mechanism, the ultimate result is the formation of allyloxy groups which serve as monofunctional initiators, the presence of which lowers the theoretical functionality of the polyol. Recently, the development of unsaturation during polyoxyethylation has been established. See, for example, U.S. Pat. No. 4,764,567.
The magnitude of unsaturation and amount of monol in the polyol increases rapidly with increasing molecular weight. Thus, as Ceresa points out on page 20, a polyoxypropylene monol having a molecular weight of 608 had an unsaturation of 0.0063 meq/mole polyol corresponding to 0.0038 moles of unsaturation per mole of polyol, while an identically prepared monol but having a molecular weight 3.3 times higher had an unsaturation 6.3 times higher. As many polyurethane polyols, particularly those for use in flexible foams have molecular weights considerably in excess of 2000, unsaturation becomes a serious problem. For example, a commercial polyether polyol having a molecular weight of 5000, initiated with trimethylolpropane, should ideally have no unsaturation and a functionality of 3. Instead, such polyols typically have unsaturation of 0.068 meq/g polyol, and a functionality of only 2.3, attesting to the large amount of monol present.
Attempts to reduce unsaturation have centered on changing the reaction conditions such as the oxirane addition temperature and the amount and nature of catalyst. Cesium hydroxide and basic barium and strontium catalysts have proven effective, for example. However, in general, no decrease in the unsaturation due to variations in the initiator have been noted.
In addition to lowering the functionality, unsaturation in urethane polyols creates other problems such as development of odor bodies through oxidation, and development of scorch or discoloration during foaming of slabstock. Thus polyether polyols having lower unsaturation than those presently available are desirable.
Polyurethane foams are generally blown with chlorofluorocarbons or mixtures of chlorofluorocarbons and water. All-water-blown foams are rare because of shrinkage and collapse which may occur during foaming, and the change in foam physical properties caused by the presence of large quantities of urea linkages. This is especially true in the flexible foam area where the relatively stiff urea segments produce harder foams which tend also to be non-resilient.
The Montreal Protocol, signed by 24 countries in September of 1987, calls for decreasing chlorofluorocarbon (CFC) use by 50 percent by 1998. However, NASA's Ozone Trends Panel has indicated that even this lowering of CFC use may well be too little, too late. Thus at present, considerable research has been directed to preparing polyurethane foams which require no CFC's or at least reduced levels of CFC's for blowing.